Power Factor (PF) is a measure of how well an electric or electronic load resembles an ideal resistor. A power factor of “1.0” means that the load looks, from the power supplier's perspective, like a resistor. The power supply current of a load with PF=1 would be precisely proportional to the power supply voltage. In practice all electrical loads have a reactive component, inductive or capacitive, that cause the power factor to be less than 1.0. These reactive components cause the power supply current to lead or lag the power supply voltage. In addition to reactive components in many electrical loads, many also have some non-linear components that add harmonic content to the power supply current.
Power transfer from the power company to electrical load is most efficient if the power factor of the load is “1.0”. However, in reality, all real loads have PF less than one. In the case of reactive loads the reactive current is not completely dissipated in the load. but it does cause increased power dissipation in the cables used to carry the current from the power company to the load. The problem is so severe that power companies need to add large reactive loads (usually capacitive components) to their transmission system in order to compensate for loads (usually inductive) with poor power factor. The other problem of low power factor loads from the perspective of a power company is that if the PF drops from 1.0 to 0.5 then the power company must double its generating capacity because generators are sized by their VA rating and not by their wattage rating. A high power factor grid means that fewer power plants need to be built.
With reference to FIGS. 1A and 1B, many electronic devices 1 include a full bridge rectifier 10 as part of their power supply module. The full bridge rectifier 10 is responsible for rectifying the Alternating Current (AC) voltage from AC power source 11 to the pulsating Direct Current (DC) voltage that is then further modified before eventually supplying load 12. These bridge rectifier loads (also known as non-linear loads 12) produce power supply current waveforms that are not proportional to the power supply voltage. The power supply current, as shown in FIG. 1B, looks more like a series of spikes 14. The spikes 14 are not exactly symmetrical with the power supply voltage waveform 13 because the voltage drop on the holding capacitor C is different at the leading and trailing edges of the current waveform 15.
With reference to FIG. 1C, a known circuit illustrated by the circuit in FIG. 1A is further connected with an active power factor correction circuit 16 for increasing power factor. The circuit, as shown in FIG. 1C, comprises a power factor correction circuit 16 having a power factor correction controller 161, a switch TR, a inductance L and a diode D. The power factor correction circuit 16 measures the pulsating DC voltage as well as the current and adjusts the switching time and duty cycle to present an in phase voltage and current.
There are many examples in the literature where active power factor correction circuitry can be added to electronic circuits for improving power factor. Such power factor correction circuitry works well, but it can only improve the power factor of newly installed electronic devices; it cannot improve the power factor of electronic devices with poor power factor that have been already installed.
Some Exemplary Embodiments
These and other needs are addressed by the exemplary embodiments, in which one approach provides for compensating electronic devices with better power factor.
Another approach is provided for improving power factor of a traditional electronic device that has already been installed.
According to one embodiment, a power factor compensating method compensates a power factor of a traditional electronic device connected to a power source, and the electronic device is a type of a non-linear load. The power factor compensating method enables a compensator to receive a supply voltage from the power source commonly connected to the traditional electronic device and disables a load in the compensator for a certain period relative to the supply voltage. The period corresponds to a range that makes an overall supply current more proportional to the supply voltage.
In one embodiment, the disabling period corresponds to a range that covers a peak of the supply voltage waveform.
Compared to the power factor of the traditional electronic device connected to the power source, the power factor compensating method with the exemplary embodiments provides compensation on areas of the supply current waveform where the current of the electronic device is not proportional to the supply voltage from the power source. This improves the power factor of the traditional electronic device from the perspective of a power company.
Still other aspects, features and advantages of the exemplary embodiments are readily apparent from the following detailed description, by illustrating a number of particular embodiments and implementations, including the best mode contemplated for carrying out the exemplary embodiments. The exemplary embodiments are also capable of other and different embodiments, and their several details can be modified in various obvious respects, all without departing from the spirit and scope of the exemplary embodiments. Accordingly, the drawings and description are to be regarded as illustrative, and not as restrictive.